1. Field of the Invention
The invention relates in general to an electro-thinning apparatus for removing excess metal from the surface metal layer of the substrate and the removing method using the same, and more particularly to an electro-thinning apparatus capable of continuously removing excess metal from the surface metal layer of the substrate without contacting the surface and a removing method using the same.
2. Description of the Related Art
As lightweight, thinness, compactness, and high efficiency have become universal requirements of consumer electronic and communication products, the chips used in the above products need to be excellent in electronic properties, versatile in functions and small in size. Along with the maturity in chip-size package (CSP) technology, system in package (SiP) has become the mainstream in package technology. System in package integrates chips of different functions, passive components and other modules together, so that the electronic products have versatile functions. System in package also includes different technologies such as 2-dimensional multi-chip module package and 3-dimensional stacked package which stacks chips of different functions for saving space. Under the trend of reducing the overall size, the pitch between integrated circuits becomes smaller and smaller, and it is more and more difficult to achieve high-efficiency wiring on the substrate. Thus, the design of embedding passive components or circuits into the substrate is provided, and the carrier possessing electrical property is called the integrated substrate or the functional substrate.
The step of thinning or planarizing the conductive material by removing excess conductive material is an indispensible step in the manufacturing process, no matter the electronic products adopt a conventional substrate (such as printed circuit board), or an embedded passive component and/or an embedded-trace substrate. The current methods of removing excess conductive material such as mechanical grinding, chemical solution erosion, chemical mechanical polishing (CMP), or contact electrolysis all have disadvantages.
A conventional manufacturing process using two planarizing methods is exemplified below. The mechanical grinding method is used for thinning excess conductive material first, and then a chemical solution is used for etching the excess metal so that the conductive material is planarized.
Referring to FIG. 1˜FIG. 3B. FIG. 1 shows a thick metal layer being thinned according to a conventional method of mechanical grinding. FIG. 2A˜FIG. 2D show the metal layer of FIG. 1 being thinned according to multiple steps of grinding. As indicated in FIG. 1 and FIG. 2A˜FIG. 2D, the dielectric layer pattern 120 on the substrate 110 (such as a printed circuit board PCB) is covered by a thick metal layer 130, and a grinding wheel 140 rotates with respect to the surface of the metal layer 130 at a high speed to incur many flash grinding on the surface of the metal layer 130. The lines 2A˜2D of FIG. 1 denote the positions of different grindings incurred on the surface of the metal layer 130 by the grinding wheel 140. The surfaces of the metal layer after grinding are respectively illustrated by the surfaces 130a˜130d of FIG. 2A˜FIG. 2D. After mechanical grinding, the bumping surfaces as indicated in FIGS. 1, 2A and 2B are planarized as shown in FIG. 2C. To make the subsequent planarization process (such as chemical etching) easier, the surface 130c of the metal layer continues to be thinned and at last becomes the surface 130d as indicated in FIG. 2D. Then, the element of FIG. 2D, which has been through the mechanical grinding process, is immersed in a container containing an etching solution 150 as indicated in FIG. 3A, and the excess metal layer is etched by the etching solution 150. Finally, as indicated in FIG. 3B, the metal layer is planarized after chemical etching process, that is, the metal layer surface 130d is substantially aligned with the surface of the dielectric layer pattern 120.
However, there are grinding residues generated during the mechanical grinding process of removing excess conductive material. If the grinding force is not uniformly applied to the element due to the grinding residues, the element may be deformed, scratched or cracked. The method of chemical erosion can only planarize the surface of the element to a certain degree, and the etching stop point is hard to control. Also, it is difficult to precisely etch the selected region and switch the etching targets optionally.
The chemical mechanical polishing (CMP) method, which combines the method of mechanical grinding and the method of chemical erosion. A to-be-processed piece is pressed on an elastic pad (the grinding pad) which is rotating. By means of relative-movement polishing technology, an erosive solution is provided to the to-be-processed piece. While the to-be-processed piece is eroded, a polishing material with micro-wear particles whose diameter is less than 100 nanometers is provided on the targeted area for selectively grinding the to-be-processed piece. Thus, the method combining chemical erosion and mechanical grinding is so called chemical mechanical polishing (CMP). The CMP method inherits both disadvantages of the methods of mechanical grinding and chemical erosion, such as particles pollution, grinding residue, slurry residue, occurrences of scratch, crack, recess, erosion and void, and less reliability of manufacturing process, all have considerable effects on the yield rate of the devices.